| 摘要 |
A wheel assembly attached to, or integrally formed with, the underside of an object for allowing the object to roll in one of at least two rolling directions includes a fixture and a wheel. The fixture has a first pair of spaced-apart axle mountings defining between them a first axial direction perpendicular to a first rolling direction, and a second pair of spaced-apart axle mountings defining between them a second axial direction perpendicular to a second rolling direction. The wheel has an axial projection extending from each side. The axle mountings and the axial projections are configured such that the wheel can be located with the axial projections retained by the first pair of axle mountings for allowing the object to roll in the first rolling direction, and alternatively, with the axial projections retained by the second pair of axle mountings for allowing the object to roll in the second rolling direction.
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